This is an overview providing 10 Linux open-source replacements for various commercial power tools, most of them available only on Windows.

Computer-Aided Design: AutoCAD
Replacement: QCAD
It’s true, QCAD has some paid plug-ins, but they can be removed very easy and QCAD will offer most of AutoCAD’s features in a similar fashion, but with an interface that is maybe 10 times faster. The good thing about QCAD is that those who are used to AutoCAD can make the transition pretty easily, since QCAD has similar syntax for commands, and similar menu entries.